Absorbent structures, such as sanitary napkins used for feminine hygiene purposes, having an elongated absorbent core covered on the body contacting side with a body fluid pervious facing which is potentially hydrophobic and covered on the garment contacting side by an impervious sheet is known in the art. The pervious facing can be either an apertured film or a non-woven material and the impervious sheet can, for example, be a polyethylene film. The absorbent core is generally made of cellulosic fibers, such as paper derived fibers called fluff which are obtained by dry stripping fibers from a paper pulp sheet. The absorbent core can also be made out of sphagnum or any other conventionally used absorbent material.
The above type of absorbent structures have been the subject of numerous research efforts aimed at obtaining a clean and dry contact surface through the appropriate choice of a fluid pervious facing material and through improving the facing's absorption properties by creating one or more channels in the upper surface of the absorbent core. The following references can be cited respectively in this regard: U.S. Pat. No. 3,695,269; U.S. Pat. No. 3,814,101; and EP-A-172,420; U.S. Pat. No. 4,184,498 and EP-A-137,725.
None of these absorbent structures, however, have provided complete satisfaction with regard to the two problems addressed by the studies.
EP-A-173,068 describes a sanitary napkin aimed at reducing both of the above-mentioned defects of sanitary napkins which are produced in a conventional manner, i.e., the staining and/or wetting of the upper facing and the poor distribution of fluids throughout the absorbent core. The sanitary napkin described in EP-A-173,068 includes an elongated absorbent core having an upper or body contacting surface and a bottom or garment contacting surface. The absorbent core is hollowed out in the body contacting surface by means of at least one elongated groove which forms a channel suitable for transporting body fluids, usually in a longitudinal direction. The sanitary napkin has, among other things, a hydrophobic facing which is pervious to body fluids and which covers the body contacting surface containing the hollow channel. For the body contacting surface to remain dry and clean when using a hydrophobic facing, the facing must extend down into the channel and be attached to the bottom of the channel (page 4, line 15-31). If the facing overlies the channel, contrary to the teaching of EP-A-173,068, the objectives sought will not be obtained and unfavorable results are observed from both the aesthetic and functional points of view (page 4, line 31 to page 5, line 2). The channel width and depth are stated to not be critical so long as the dimensions are adequate to insure its fluid transporting function (page 8, lines 22-25). The sanitary napkin described and shown in the example only utilizes a single channel which is located in the center of the body contacting surface. Such a sanitary napkin has turned out to be unsatisfactory because the channel hollowed out in the upper surface produces a rigidity to the structure which is prejudicial to the user's comfort.